A plague decimates 90 percent of the world's population. The survivors are not so lucky: Half mutate into genetic "abominations" that haunt and hunt the characters of Portland writer Alex Adams' chilling debut novel, "White Horse."

The sickness begins with vomiting, which Zoe Marshall, 30, is busy doing as she makes her way across Italy in desperate hope of a rendezvous in Greece. (Her ailment reveals itself to be a transformation of a different color.)

The virus gets its name from a preacher's apocalyptic patter that warns the "first seal is opened and the white horse has come with its deadly rider to test us with Satan's disease."

But as is usually the case, mankind is its own worst enemy.

Zoe's narrative alternates between a mundane "Then" fast converging with a horrific "Now." Nineteen months earlier, a sealed jar inexplicably shows up in her apartment. Fearing loss of her sanity, Zoe meets with a therapist, Dr. Nick Rose, and a friendship emerges.

Zoe cleans floors at Pope Pharmaceuticals, where tedium dissipates the day the lab mice turn up dead. Soon she notices her neighbors falling ill. Their cats disappear all at once. The deaths begin.

Fast-forward. Rain falls constantly, aftershocks of wars waged with weather modification -- science gone awry. Electronic warfare wipes out technology, while boots-on-the-ground invasions kill those who might have otherwise survived White Horse. Even the president of the United States becomes just another faceless refugee.

In the now, money no longer exists: The currency is blood and pills. Food stores have largely spoiled, though there is plenty of shelter. "Whoever said processed foods were bad hadn't vacationed at the end of the world," Zoe says.

Zoe clings to some semblance of humanity, an outlook tempered with her mordant sense of humor and the grim reality of survival. "Holiday snapshots from rainy Italy: corpses, mutilation, rotting flesh," she says.

Unlike some others, she extends help to those she meets, beginning with Lisa, a blind girl abused by her father and uncle. "I won't let this one come to harm when I've lost so many along the way," Zoe tells herself.

But in this time, harm doesn't wait for invitations, presenting itself as a cruel doctor known as "Swiss," who co-opts Zoe and Lisa's journey. This doctor becomes another disease from which there seems to be no escape, even as Zoe draws nearer to her destination in Greece.

"White Horse" is the first installment in a proposed trilogy from Adams, a New Zealand native. It draws to a compelling pause, with a pair of revelations in the final pages that should spur readers to a sequel.

Adams has fashioned a macabre landscape in which she explores fundamental questions about what it means to be human, with a compelling protagonist and narrator as our guide.

While navigating "pieces and places of people who were once whole," Zoe wrestles with the inner turmoil of her heart. Life goes on, as does living.